Telecommunications and other network providers continually strive to increase the traffic carrying capability of their transmission medium. As a result, greater bandwidth media, such as fiber optic cables, are increasingly employed. Unfortunately, if one or more of the fiber optic cables fail, massive disruption of services to a large number of network customers and users can result. Network service providers or telecommunications carriers therefore strive to quickly and economically restore traffic effected by these disruptions or "outages." Restoring network outages generally requires four steps: (1) detecting the network failure, (2) isolating the location of the failure in the network, (3) determining a traffic restoral route, and (4) implementing the restoral route. Network restoration must be executed quickly to ensure minimal interruption of network traffic. Therefore, nearly all telecommunications carriers wish to restore traffic within a few seconds or less.
Telecommunications carriers typically simulate possible failures, determine restoral routes and develop a "pre-plan" by collecting large amounts of data reflecting the logical topology of the network, and then analyze this data. The collected data is often retrieved from network engineering databases which reflect the logical construction of the network, such as indicating the connections and paths of all network traffic trunks. An engineer or network analyst analyzes the collected data, compares the collected data to the geographic or physical layout location of the network, and then generates the pre-plans therefrom.
Since the number of possible failures in a network necessarily increases as the size of the network increases, a large number of pre-plans are required. Furthermore, as a network grows, pre-fabricated restoral plans or pre-plans must be continually reevaluated, and new pre-plans created. To overcome the lack of updated data in pre-plan restoration methods, dynamic restoration methods have been developed. Dynamic restoration methods formulate a restoral route dynamically, during the restoration process and when a failure is detected, so that the method employs the most accurate and recent network data available.
Under either restoration method, the restoration route is typically established by interconnecting a number of spare links through different nodes of the network so that traffic may be rerouted through those spare links. These spare links may be referred to as spare capacity and they are purposely added to the telecommunications network for restoration. For economic considerations, this spare capacity is limited. Thus, if after restoration, the network were to remain in the topology with the previously spare links now carrying traffic, the network may less effectively restore traffic due to other failures. In other words, the spare capacity provides a safety margin for restoration. Yet once the spare capacity or some portion of it has been used, the safety margin could be severely diminished unless the topology of the network is restored to its normal state, i.e., prior to the failure.
Currently, once a fiber is repaired following an outage, technicians manually reconnect the different working and spare links at each cross-connect switch of the telecommunications network. The technicians refer to the pre-plan and follow instructions therein to connect/disconnect various ports at each of the cross-connect switches affected by the malfunctioned fiber to return the switch to its pre-failure state. This process is quite laborious and is subject to operator mistakes, and requires a substantial amount of repair time.
Under an alternative method of normalizing the network following restoration, a centralized system or computer employs a patch-and-roll method. Under the patch-and-roll method, the two end nodes of the restoral route transmit signals to each other over both restoral route and over the now fixed original traffic route. Each of the end nodes confirms transmission of the signals over the fixed traffic route, and thereafter, each end node switches to receive signals from their restoral route to the fixed traffic route. Each end node then stops transmitting over the restoral route. The centralized system, such as an operations support systems network (OSSN), performs the various tasks and issues commands to the end nodes. The OSSN, however, necessarily requires time to perform the patch-and-roll method and issue the appropriate commands to the end nodes. Additionally, if the commands are transmitted over spare trunks in the network, these trunks can then not be used for transmitting other traffic.